| 摘要 |
<p>The device has an alarm switch (24) operated to allow two alternating tones to be provided over at least four time intervals of approximately the same length. The acoustic signal is accompanied by a visual signal provided by flashing blue lights (16,17). A transistor (32) has its collector/emitter path connected in the energising circuit of two relays (29,30) controlling respective signal horns (10,11). The transistor base is coupled via two opposing coupling diodes (35,36) to the switch contacts (18b,19b) of two current control relays (18,19) for the two signalling lights (16,17) so that the audio signal is only provided in conjunction with the visual signal. The device is used for a fire engine or other emergency vehicle.</p> |
